Fourth SpaceWalk Beckons

The crews of the Discovery and the International Space Station grappled Wednesday with a solar array that refused to fully retract, raising the possibility of an unscheduled fourth spacewalk.

For several tedious hours, astronauts, including Sweden’s Christer Fuglesang, painstakingly tried to fold up the six-year-old, 115-foot (35-meter) solar array on the ISS by remote control, but were unable to complete the job when the system jammed.

A refolding of the old array, which was used to generate electricity for the orbiting space station, is necessary to allow the new solar array to rotate to track the sun.

”A map never goes back to the way you bought it, it just doesn’t,” said John Curry, flight director for the space station.

Astronauts on the space shuttle had three spacewalks scheduled during their 12-day mission that began Saturday. The first on Tuesday was used to attach a two-tonne truss segment on the ISS.

The second and third spacewalks, on Thursday and Saturday, will be used to rewire the ISS so a solar array installed in September can be switched on to provide additional power to the station.

NASA said a fourth spacewalk may be needed to manually fold the old array but that would not take place before the third scheduled spacewalk is over on Saturday.

It was unclear whether the additional spacewalk, should it be needed, would prolong the Discovery mission beyond its scheduled return date of December 21.

The new array installed during the September mission of the space shuttle Atlantis will double the ISS’s power supply.

It was expected to be activated on Wednesday after the older array had been retracted. The older array will eventually be moved to another spot on the ISS.

Although it has not been retracted to its ideal position, NASAsaid the older array has been foreshortened enough to allow the highly complex rewiring work to proceed as scheduled during the spacewalks on Thursday and Saturday.

Discovery mission specialist Robert Curbeam and Sweden’s first astronaut Christer Fuglesang, of the European Space Agency, who performed the first space walk, were assigned Thursday’s task.

The astronauts will reconfigure and rewire the electricity and climate control of the US-made portion of the ISS from its present, temporary set-up.

During the work, power to half of the ISS will be switched off. On Saturday Curbeam and mission specialist Sunita Williams will install cameras outside the ISS expected to greatly facilitate future construction work.

A minor hiccup in the Discovery construction mission, apparently without serious consequences, happened during the first six-hour space walk, when Fuglesang lost an extender on a tool and it floated off in space.

The girder-like ISS is being assembled piece by piece. Construction resumed in September with the Atlantis mission, after a three-year hiatus following the 2003 Columbia disaster.

The Discovery mission is part of 14 shuttle flights NASA has planned over the next four years to finish the ISS by 2010, when the shuttle fleet, down to three vehicles, is to be retired.

Discovery blasted off late Saturday from Cape Canaveral, Florida – the first nighttime liftoff in four years. It docked on the station Monday and is to remain there eight days.

National Aeronautics and Space Administration engineers said two preliminary inspections carried out after takeoff and shortly before Discovery docked with the ISS found no damage to the Discovery’s heat shield during launch.

Such inspections on the shuttles have become routine since the Columbia tragedy.

Columbia’s heat shield was pierced by foam insulation that peeled off its fuel tank during lift-off, causing the shuttle to disintegrate during its return to Earth in February 1, 2003, killing all seven astronauts on board.

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